Alternator amperage

[BobbyB]

The alternator on my small block ford street hot rod started making noise, so I ought to get a new one. I currently have a flex fan, but might go to an electric fan, I have a nitrous heater and electric fuel pump that draw some current too. How many amps should the new alternator be rated for? The old one was stock replacement for a 68 mustang 390. Is there a replacement alternator with the correct pulley and amps that came on a specific ford model & year? Thanks.

[jed]

Call Quality Power they can recommend the the correct amperage and pulley size.

[jred]

I can tell you this I built a stock 289 ford engine for a 65 mustang fastback nothing special 9 to 1 very small cam of course its the middle of summer 108 degrees or more here in the desert most new engines will run hotter then usual for the first 500/1000 miles and ours was doing the same I had sent the radiator out and the radiator shop said it was good to go,, still couldn't get it to cool down to 195 or so ,,, checked for combustible gases in the radiator even looked to see if I had put a head gasket on backwards,, it also had a flex fan but no shroud ,, we decided to install a new champion aluminum radiator with electric fan and shroud well it was worse,, on top of all this the car would start out at about 200 degrees and drive around come back to the shop at about 218/220 and then not want to start if you turned it off cranks slow,, we were looking for a mechanical problem but it was and electrical problem the alternator was only putting out 65amps and the electric fan set up was taking 40 amps to run,, make sure that you more amps then you need,, the newer trucks have 160 plus amp alternators..

[BCjohnny]

How many amps should the new alternator be rated for?

As a rule of thumb, assuming your set up is fairly conventional and lacks a multitude of sensors, you really want to be at a shade over 14v with all your primary loads on at about 1600rpm engine speed, give or take

In this case bigger is usually best, within reason, the fail safe is put the highest output unit on you can fit / afford and not worry too much about it ...... any alternator will only output what the battery / load requires, once the initial charge surge of replenishing cranking draw has been accomplished

In your case around 100 amps should be more than plenty, but I'd guess 75 amps would get it done, depending on how often your bottle heater is an and it's draw

[hysteric]

Grab a bluetooth battery monitor and it will tell a lot about whats happening with your alternator and charging.

They are cheap and all the info logs to your phone. https://www.jaycar.com.au/12v-battery-m ... y/p/QP2265

Amazon: https://www.amazon.com.au/Battery-Monit ... B078JD645R

https://www.youtube.com/watch?v=gNUYlqF8h6Y

[aquartlow]

A large case 130 amp Ford 3G alternator sourced from a '94 Ford Taurus with 3.0 should fit the bill(Lester #7765). I use this exact one on my '79 Ranchero with 472 bbf and it fits great(just a bit larger then the original 1G 55-65 amp Ford alternator. I run dual electric cooling fan assembly sourced from a '95 Ford Windstar and it keeps the engine cool even in summer traffic with the A/C running. The 3G was almost a direct bolt-in(used a different alternator spacer size and exchange the serpentine belt pulley to a single V-belt pulley off your 1G alternator-may need additional spacer behind pulley for pulley to alternator case clearance) and just a bit of wiring(use the GREEN/RED STRIPE wire from voltage regulator harness to energize the alternator to charge and run at least a 4ga with 175 amp mega fuse to battery side of starter solenoid) . Doing so gets rid of the 1G alternator's voltage regulator and wiring along with it. The large case 3G puts out 80 amps at idle(alternator idle is around 2000-2400 rpm-not engine rpm, but alternator shaft rpm) and at full tilt over 150 amps.

[BCjohnny]

The 3G is a nice piece, far better than the 2G it replaced which was comparatively junk

Simple rewiring is needed, being an internally regulated machine unlike the original, but the info is available online

I'd suggest upgrading the main feed, or at least 'doubling up' the original, while your at it